Weygand mainly served as a staff officer to Ferdinand Foch in World War I. Weygand initially fought against the Germans during the invasion of France in 1940, but then surrendered to and partially collaborated with the Germans as part of the Vichy France regime before being arrested by the Germans for not fully collaborating with them.

Weygand was born in Brussels of unknown parents. He was long suspected of being the illegitimate son of either Empress Carlota of Mexico (by General Alfred Van der Smissen); or of her brother Leopold II, King of the Belgians, and Leopold's Polish mistress. Van der Smissen always seemed a likely candidate for Weygand's father because of the striking resemblance between the two men. In 2003, the French journalist Dominique Paoli claimed to have found evidence that Weygand's father was indeed van der Smissen, but the mother was Mélanie Zichy-Metternich, lady-in-waiting to Carlota (and daughter of Prince Metternich, Austrian Chancellor). Paoli further claimed that Weygand had been born in mid-1865, not January 1867 as is generally claimed.[1]

Regardless, throughout his life Weygand maintained he did not know his true parentage. While an infant he was sent to Marseille to be raised by a widow named Virginie Saget, whom he originally took to be his mother.[2] At age 6 he was transferred to the household of David Cohen de Léon, a financier of Sephardic origins who was a friend of Leopold II. Upon reaching adulthood, Weygand was legally acknowledged as a son by Francois-Joseph Weygand, an accountant in the employ of M. Cohen de Léon, thereby granting him French citizenship.

In his memoirs he says little about his youth, devoting to it only 4 pages out of 651. He mentions the gouvernante and the aumônier of his college, who instilled in him a strong Roman Catholic faith. His memoirs essentially begin with his entry into the preparatory class of Saint-Cyr Military School in Paris, as if he had wished to disregard his connection with Mme. Saget and M. Cohen de Leon.

He was admitted to the École Spéciale Militaire de Saint-Cyr, under the name of "Maxime de Nimal" as a foreign cadet (Belgian). Graduating in 1887, he was posted to a cavalry regiment. After changing his name to Weygand and receiving French nationality, he became an instructor at Saumur.

During the Dreyfus affair, he was one of the most antidreyfusard officers of his regiment, supporting the widow of Colonel Henry, who had committed suicide after the discovery of the falsification of the charges against Captain Dreyfus.

Once promoted to Captain, Weygand chose not to attempt the difficult preparation to the École Superieur de Guerre (the French staff college) because of his desire, he said, to keep contact with the troops. This did not prevent him from later becoming an instructor at the Cavalry School at Saumur. He was one of the few to attend the Centre des Hautes Etudes Militaires (a school to give more strategic instruction), set up in the spring of 1909,[3] despite not having been "breveté" (passed staff college).[4]

Along with Joffre and Foch, Weygand attended the Russian manoeuvres in 1910; his account mentions a great deal of pomp and many gala dinners, but also records Russian reluctance to discuss military details.[5] As a Lieutenant-Colonel Weygand attended the last prewar French maneoeuvres, in 1913, and commented that had revealed “intolerable insufficiencies” such as two divisions becoming mixed up.[6]

Weygand passed World War I as a staff officer. At the outbreak, he satisfied his taste for contact with the troops by spending 26 days with the 5ème Hussars. On 28 August, he joined the staff of General Ferdinand Foch, under whom he was to serve for much of the rest of the war.

Weygand was promoted to Général de Brigade in 1916. He later wrote of the Anglo-French Somme Offensive in 1916, at which Foch commanded French Army Group North, that it had seen “constant mix-ups with an ally [i.e. the British] learning how to run a large operation and whose doctrines and methods were not yet in accordance with ours”.[7]

British Prime Minister Lloyd George pushed for the creation of a Supreme War Council, which was formally established on 7 November 1917. Keen to sideline the British CIGSGeneral Robertson, he insisted that, as French Army Chief of the General Staff, Foch could not also be French Permanent Military Representative (PMR) on the SWC.[8]Paul Painlevé, French Prime Minister until 13 November, believed that Lloyd George was already pushing for Foch to be Supreme Allied Commander so wanted him as PMR not French Chief of Staff.[9]

The new Prime Minister Georges Clemenceau wanted Foch as PMR to increase French control over the Western Front, but was persuaded to appoint Weygand, seen very much as Foch's sidekick, instead.[10] Clemenceau told President Wilson's envoy Colonel House that he would put in a “second- or third-rate man” as PMR and “let the thing drift where it will”.[11]

However, Clemenceau only agreed to set up an Allied General Reserve if Foch rather than Weygand were earmarked to command it. The Reserve was shelved for the time being at a SWC Meeting in London (14–15 March 1918) as the national commanders in chief, Philippe Pétain and Haig, were reluctant to release divisions.[10]

Weygand was in charge of Foch's staff when his patron was appointed Supreme Allied Commander in the spring of 1918, and was Foch's right-hand man throughout his victories in the late summer and until the end of the war.

Weygand initially headed a small staff of 25-30 officers, with Brigadier-General Pierre Desticker as his deputy. There was a separate head for each of the departments, e.g. Operations, Intelligence, Q (Quartermaster). From June 1918 onwards, under British pressure, Foch and Weygand poached staff officers from the French Commander-in-Chief Philippe Petain (Lloyd George’s tentative suggestion of a multinational Allied staff was vetoed by President Wilson). By early August Colonel Payot (responsible for supply and transport) had moved to Foch’s HQ, as had the Military Missions from the other Allied HQs; in Greenhalgh’s words this “put real as opposed to nominal power into Foch’s hands”. From early July onwards, British military and political leaders came to regret Foch’s increased power, but Weygand later recorded that they had only themselves to blame as they had pushed for the change.[14]

Like Foch and most French leaders of his era (Clemenceau, who had lived in the USA as a young man, was a rare exception), Weygand could not speak enough English to “sustain a conversation” (German, not English, was the most common second language in which French officers were qualified). Competent interpreters were therefore vital.[15]

Weygand drew up the memorandum for the meeting of Foch with the national commanders-in-chief (Haig, Petain and John J. Pershing) on 24 July 1918, the only such meeting before the autumn, in which Foch urged (successfully) the liberation of the Marne salient captured by the Germans in May (this offensive would become the Second Battle of the Marne, for which Foch was promoted Marshal of France), along with further offensives by the British and by the Americans at St Mihiel.[16] Weygand personally delivered the directive for the Amiens attack to Haig.[17] Foch and Weygand were shown around the liberated St. Mihiel sector by Pershing on 20 September.[18]

Weygand later (in 1922) questioned whether Petain’s planned offensive by twenty-five divisions in Lorraine in November 1918 could have been supplied through a “zone of destruction” through which the Germans were retreating; his own and Foch’s doubts about the feasibility of the plans were another factor in the seeking of an armistice.[19] In 1918 Weygand served on the armistice negotiations, and it was Weygand who read out the armistice conditions to the Germans at Compiègne, in the railway carriage. He can be spotted in photographs of the armistice delegates, and also standing behind Foch's shoulder at Pétain's investiture as Marshal of France at the end of 1918.

Weygand travelled to Warsaw expecting to assume command of the Polish army, yet those expectations were quickly dashed. He had no good reply for Józef Piłsudski, who on 24 July during their first meeting asked "How many divisions do you bring?" Weygand had none to offer. From 27 July Weygand was an adviser to the Polish Chief of Staff, Tadeusz Jordan-Rozwadowski. It was a difficult position; most Polish officers regarded him as an interloper, and spoke only Polish, which he did not understand. At the end of July he proposed that the Poles hold the length of the Bug River; a week later he proposed a purely defensive posture along the Vistula River; both plans were rejected, as were most of his other suggestions. One of his few lasting contributions was to insist on replacing the existing system of spoken orders by written documents. Norman Davies writes: "on the whole he was quite out of his element, a man trained to give orders yet placed among people without the inclination to obey, a proponent of defence in the company of enthusiasts for the attack."[20] During another meeting with Piłsudski on 18 August, Weygand became offended and threatened to leave, depressed by his failure and dismayed by Poland's disregard for the Triple Entente. At the station at Warsaw on 25 August he was consoled by the award of the Virtuti Militari, 2nd class, Poland's highest military decoration; at Paris on the 28th he was cheered by crowds lining the platform of the Gare de l'Est, kissed on both cheeks by the Premier Alexandre Millerand and presented with the Grand Cross of the Legion of Honour.[20] He could not understand what had happened and has admitted in his memoirs what he said to a French journalist already on 21 August 1920: that "the victory was Polish, the plan was Polish, the army was Polish".[21] As Norman Davies notes: "He was the first uncomprehending victim, as well as the chief beneficiary, of a legend already in circulation that he, Weygand, was the victor of Warsaw. This legend persisted for more than forty years even in academic circles."[20]

Weygand was unemployed for a time after the military mission to Poland, but in 1923 he was made commander-in-chief Levant, the French mandate in Lebanon and Syria. He was then appointed High Commissioner of Syria the next year, a position he also only kept for a year.

Weygand returned to France in 1925, when he became director of the Center for Higher Military Studies, a position he had for five years. In 1931 he was appointed Chief of Staff of the French Army, Vice President of the Supreme War Council and Inspector of the Army, and was elected a member of the Académie française (seat #35). He remained in the positions, except Inspector of the Army, until his retirement in 1935 at 68.[22]

He was recalled for active service in August 1939 by Prime Minister Édouard Daladier and appointed commander-in-chief for the Orient Theatre of Operation.

By late May 1940 the military disaster in France after the German invasion was such that the Supreme Commander—and political neutral—Maurice Gamelin, was dismissed, and Weygand—a figurehead of the right—recalled from Syria to replace him.

Weygand arrived on 17 May and started by cancelling the flank counter-offensive ordered by Gamelin, to cut off the enemy armoured columns which had punched through the French front at the Ardennes. Thus he lost two crucial days before finally adopting the solution, however obvious, of his predecessor. But it was by then a failed manoeuvre, because during the 48 lost hours, the German infantry had caught up behind their tanks in the breakthrough and had consolidated their gains.

Weygand then oversaw the creation of the Weygand Line, an early application of the Hedgehog tactic; however, by this point the situation was untenable, with most of the Allied forces trapped in Belgium. Weygand complained that he had been summoned two weeks too late to halt the invasion.[23] After some further vain attempts to contain the enemy offensive, he then joined in seeking an armistice and cooperation with the German occupiers.

While there, he convinced the young officers, tempted to resistance, of the justice of the armistice, by letting them hope for a later resumption of combat. He deported opponents to concentration camps in Southern Algeria and Morocco. There, he locked up, with the complicity of Admiral Jean-Marie Charles Abrial, adversaries of the Vichy regime (Gaullists, Freemasons and Jews. He also arrested communists, despite their non-support for the resistance ordered by Moscow at the time.), the foreign volunteers of Légion Etrangère, foreign refugees without employment (but legally admitted into France) and others. He applied Vichy's laws against Jews very harshly (see Vichy France). With the complicity of the Recteur (University chancellor) Georges Hardy, Weygand instituted, on his own authority, by a mere "note de service n°343QJ" of 30 September 1941, a school "numerus clausus" (quota), driving out from the colleges and from the primary schools most of the Jewish pupils, including small children aged 5 to 11. Weygand did this without any decree of Marshal Philippe Pétain, "by analogy," he said, "to the law about Higher Education."

Weygand acquired a reputation as an opponent of collaboration when he protested, in Vichy, against the Protocols of Paris of 28 May 1941 signed by Admiral François Darlan, agreements which granted bases to the Axis in Aleppo, Syria, Bizerte, Tunisia and Dakar, Senegal and envisaged an extensive military collaboration with Axis forces in the event of Allied countermeasures. As Simon Kitson demonstrated in his book The Hunt for Nazi Spies, Weygand remained outspoken in his criticism of Germany.[24]

Nevertheless, the Weygand General Delegation (4th Office) collaborated with Germany by delivering to Erwin Rommel's Afrika Korps 1200 French trucks and other French army vehicles (Dankworth contract of 1941), as well as heavy artillery pieces accompanied with 1000 shells per gun.

Weygand was apparently favorable to collaboration with Germany, but with discretion. Additionally, when he opposed German bases in Africa, he did not intend to be neutral or to help the Allied camp, rather he only sought to prevent France from losing prestige with the natives and keep its colonial empire. Nevertheless, since Adolf Hitler demanded full unconditional collaboration, he pressured the Vichy government to obtain the dismissal and recall of Weygand in November 1941. One year later, in November 1942, following the Allied invasion of North Africa, Weygand was arrested. He remained in confinement in Germany and then in the Itter Castle in North Tyrol with General Gamelin and a few other French Third Republic personalities until May 1945, when he fell into the hands of the Americans after the Battle for Castle Itter.

After returning to France, he was held as a collaborator at the Val-de-Grâce but was released in May 1946 and cleared in 1948. He died in Paris at the age of 98. He had married Marie-Renée, the daughter of Brigadier General Viscount de Forsanz, of Brittany. They had a younger son Jacques.